Thermal cyclers are common devices in chemical, in particular, in biochemical laboratories. They are, e.g., used to facilitate a variety of processes for creation and/or detection of molecules like, i.e., nucleic acid sequences for research, medical or industrial purposes. Processes that can be performed with thermal cyclers include, but are not limited to, amplification of nucleic acids using procedures such as the polymerase chain reaction (PCR), real-time polymerase chain reaction ((q)PCR), ligation chain reaction (LCR), high resolution melting curve (HRM) evaluation and melting curve (RM) investigation. In particular, amplification processes are used to increase the amount of a target sequence present in a nucleic acid sample while in real-time PCR, the change in amplicon amounts is monitored. Further, with HRM and MC, the denaturation or re-naturation of specific amplicons, targets or molecules may be monitored.
In order to detect the amount of a desired target sequence achieved in the samples, fluorescent labels may be used. Fluorescent labels are substances which are capable of absorbing light and emitting a light signal at a different wavelength. Some types of fluorescent labels are active in the presence of a target sequence, such that a fluorescence response from a sample is indicative of the presence and amount of the target sequence. Commonly, in order to monitor the amount of a desired target sequence, the samples are removed from the thermal cycler and put into an excitation light beam. As such a mode of detection implies that the sample is removed from the thermal cycler, e.g. US-2011/0160073 A1, in contrast, suggests to use a movable fluorescence detection module which is put on top of a thermal cycler. The detection module comprises an excitation light generator and an emission light detector that are attached to a shuttle movably mounted on a support structure. Hence, the excitation light generator and emission light detector may conveniently be positioned over the individual sample wells of the thermal cycler to detect the fluorescence response on line, i.e. during the temperature cycling.
However, with the thermal cycler comprising a large reaction zone with a plurality of sample wells, the temperature may be different in different sample wells. As the temperature severely influences the processes inside the samples, reaction rates may be different in different sample wells. It is thus desirable to investigate the spatial temperature distribution within a reaction zone of the thermal cycler. Further, it is desirable to control the heating of the reaction zone of the thermal cycler, such that a desired temperature is achieved in individual sample zones. In addition, it is desirable to provide a way to check if the optics, the optical detector and/or the excitation light source of the thermal cycler are correctly positioned, aligned and functional for each individual sample position and to provide calibration information for any occurring misalignment.
In EP 2 108 942 A1, a system for the optical detection of light from analytical samples is disclosed. The system comprises an analytical instrument comprising an optical detection unit and a sample block unit. The system further comprises a calibration device for calibrating the optical detection unit of the analytical instrument. The calibration device comprises an electrically powered reference light source emitting light that is detected by the optical detection unit. Moreover, in U.S. Pat. No. 6,852,986 B1, a fluorometer is disclosed that is combined with a thermal cycler. The fluorometer features a light emitting diode having a one-to-one correspondence to each of the plurality of sample containers, such as capped PCR tubes in a standard titer tray. The fluorometer further comprises an optical path between each LED and its correspondingly positioned container, and another optical path between each fluorescing sample within the positioned container and an optical signal sensing means.